I saw this video a few years back and thought it was amazing. I came across it again the other day and thought that anybody involved in solar should see it.

Enjoy.

http://www.youtube.com/watch?v=lFJc4xuFPcc

When installing a pressurized solar heating system an issue that the installer must be concerned about is getting the air out of the system.  If the installer leaves too much air in the propylene glycol/water solution they can have all kinds of problems including: pump cavitation, vapor lock, air lock, unwanted system noise, decrease in efficiency, overheating and premature system discharge.  None of these conditions are desirable.  The question then is how do you insure that you adequately purge the air from the system.  The process isn’t difficult although you can’t take any shortcuts and achieve consistent results.

1. After installing the solar panels in the sun make sure that you cover the panels.  You want to charge the system when the panels are cold and the sun is not on them.  You can either charge in the morning, evening or cover the panels when installing and charge it whenever you get around to it.
2. Determine the pressure that you will be charging the system to.  This should be 15 psi + 5 psi for every 10 feet (story) that the top of the collectors are above the pressure gauge, i.e. A system that has the panels installed on top of the second story and the tank is the in garage would charge to 15 + (2 x 5) = 25 psi
3. Make sure that the expansion tank is charged to the number determined in step 2 above.
   

Note:   A pressurized glycol system should have at a minimum the following components: a fill port, a check valve, and a drain port.  The closer the fill port and drain port are located to each other (with check valve or ball valve in between) the easier it will be to purge air from the system.
4.  Pre-mix your glycol to the appropriate ratio for your location in a bucket.
5.  Using three hoses connect 1 – from the bucket to the supply of the transfer pump, 2- from the transfer pump to the charge port of your solar system, and 3 – from the drain of your solar system back to the bucket.
6. Prime the pump
7. Open the valves to both the charge and drain port and turn the pump on.  You should see the fluid level in the bucket diminish as the pump pushes glycol from the bucket through the supply piping, collectors, return piping and finally back into the bucket.  After you start to see the fluid pump around you will want to let the pump run for another minute or so before you turn the pump off.  **** Caution – The hose ends in the bucket should always remain below the fluid level during the whole charging procedure.  Close the fill and drain valve.
8.  Wait until the foam in the bucket completely dissipates (this should take 4 –5 minutes).
9.  Repeat step #7 as many as 4 or five times until you no longer see bubbles or foam entering the bucket as the pump is running.  Once you confirm that the system is running with no foam or bubbles entering the bucket after running for a minute then CLOSE THE DRAIN VALVE.
10.  Keep the tranfer pump running until the desired system pressure (determined in step #2) is reached on the system pressure gauge.  Once the desired pressure is reached then close the fill valve.
11.  Disconnect the hoses to the solar fill valve and drain valve.

You are now ready to turn on your solar heating system.

Although you have done an excellent job eliminating the air as you charged the system you haven’t got it all.  The mixture of propylene glycol and water contains some air in solution.  As the solution heats up the air in solution is squeezed out of solution.  This additional air will accumulate in your system as your system repeatedly heats up and cools down.  Once this air has left solution it will not re-enter the solution and will travel around your system accumulating in local high points.  If your system has a place to capture and release this air then after a few weeks of running you will have a solution that has no (or a negligable amount) air trapped in the system.  With all of the air ultimately eliminated you now have a system that will operate quietly, efficiently and much more reliably.

With various types of plumbing systems whether solar heating systems, hydronic heating systems or just regular home plumbing it is common for gate type drain valves to leak (see picture 1).

The valve will often leak when it gets old or if something gets caught on the seal. Most people will just leave a small drip and not worry about it. If you have a machined cap for the drain you can install that and be done. Although getting a metal cap can sometimes be difficult and they are never right at hand. An easy solution if you have access to a plastic bottle of soda is to take the cap from the soda bottle (I know pepsi works) and screw that onto the drain. Voila a quick and easy solution to that leaking boiler drain, hose bibb, washing machine connection or drain on your solar heating system. (see picture 2)

A question we will get from time to time is “how do I know that my solar pump is running?”  There are several answers to this question so we will cover one way to know if the pump is operating properly.  When you look at it all a pump does is create a pressure differential across itself.  The pump (if working properly) will have lower pressure before the pump and higher pressure after the pump.  This pressure differential causes fluid to flow away from the higher pressure region towards the lower pressure region.  On a closed loop glycol system (or other hydronic systems) you should have the following components in addition to the pump: an expansion tank and a pressure gauge.  A properly designed system will place the expansion tank immediately prior to the inlet to the pump.  The expansion tank serves as the zero pressure change point of the hydraulic loop.  Since the expansion tank doesn’t see pressure change as flow is generated the only way for the pump to do its job (creating a pressure differential) is for the pump to create an increase in pressure on the outlet side of the pump.

This pressure increase on the outlet side of the pump can be easily observed by watching the pressure gauge when the pump is turned on and off.  Watch this video to get a better sense of what you are looking for.  The higher the head of the pump the larger the pressure spike you will see when the pump is turned on.

It seems that more and more homes that are requesting solar hot water systems are coming equipped with metal roofs.  A solar system installed on an asphalt shingle is challenging enough when it comes to getting on the roof and keeping your feet under you.  A metal roof adds a little more challenge to that issue.  An experienced solar installer offered me this tip: the next time you need to get up on a metal roof bring a bottle of sprite.  Shake the bottle and then spray the metal roof where you will be working with the sprite.  The sugar water will dry on the roof creating a tacky surface that will make it much easier to maintain traction while you are working.  The sprite will not stain the roof and will wash off the next time it rains.

Any time you can have an extra measure of safety while you are working on the roof you want to take it.

As the solar water heating business expands to the traditional trades (plumbing and HVAC) we get questions about system payback more and more.  The contractors want to understand that the systems they install will rapidly pay for themselves.  While this is an excellent question it comes laced with many pitfalls.

We can quickly go down the road of answering this question for our own satisfaction although I don’t recommend it in general.  According to “More evidence of Rational Market Values for Home Energy Efficiency” by the Appraisal Journal a home will increase in value $20 for every $1 reduction in annual energy bill.  An average solar water heating system will save a family of 4 approximately $400 per year on their energy bill.  That would mean that if a homeowner installs a system they she see an appreciation in the value of their home of $8,000.  Interestingly, that is also about the national average installed cost of a 64 ft^2 80 gallon tank freeze protected system.  You add to that the current tax incentives which include as a minimum 30% tax credit from the federal government and you now have a system that costs less than it adds in value to your home.  With this stunning fact it would seem that every homeowner that is about to sell there home should add a system simply by the pure economics.  I make the last statement a little tongue in cheek because I understand that some homeowners are concerned about the aesthetics of an installation (I am sure to discuss that later in a future post).

When it comes down to it, the economics of solar water heating are such that a homeowner get shift there assets from their bank to their home and in return get a huge chunk of cash from the government and start saving money immediately on their utility bills.  This should be a no-brainer economically.  Although the logic is clear I don’t recommend sharing this with those that question the value of solar water heating (or more likely solar energy in general).  People’s prejudices, party affiliations and biases are such that rare is the person that will listen to logic.  I would recommend to focus the selling of systems to people that are already convinced of the value of energy efficiency they can be seen all around us.  They are the people that drive hybrids, purchase high SEER air conditioning, bicycle to work, use compact fluorescent lamps, or install programmable thermostats.  The people that are ready are all around us so we need to stop focusing on the people that won’t be convinced no matter what the logic.

Another article that might be interesting is: http://www.pmmag.com/Articles/Column/BNP_GUID_9-5-2006_A_10000000000000620715